ADVANCED HIGH-PERFORMANCE MATERIALS FOR HIGHWAY APPLICATIONS

Unknown     1:01:00 AM     No comments

In the United States, there has been continuous interest and effort in developing improved highway construction materials. Until recently, the development of improved materials was focused at improving specific properties of locally available materials by using additives (admixtures, extenders, modifiers). There was no strong impetus to seriously consider replacing conventional construction materials with new materials. However, it has now been recognized that the age of limitless construction materials and the use of conventional materials in their present form is fast coming to an end, and new technologies need to be developed to continue to support the rehabilitation and reconstruction of pavements along the Nation’s highway system. Today, concerns about limited availability and sustainability are driving the search for new and advanced materials for highway construction. 

As sustainability becomes an increasingly important element in the design and construction of transportation infrastructure, approaches are continually being sought to reduce the environmental footprint of concrete, which is the most widely used construction material in the world. Although portland cement (ASTM C150) is a relatively minor constituent in concrete, it is responsible for 90 to 95 percent of the CO2 associated with concrete (Van Dam and Taylor 2009). The key to reducing the carbon footprint of concrete is therefore to reduce the amount of portland cement used, and one way of accomplishing that is through the use of alternative cement binders.

The recent adoption of ASTM C1157, Performance Specification for Hydraulic Cement (the first version of ASTM C1157 appeared in 2000), represents an important development in this area. Other portland cement specifications (both ASTM C150 and C595) are largely prescriptive, in that they are based on measured chemical and physical properties that are assumed to relate to the performance of the cement in concrete. In contrast, ASTM C1157 simply requires that the cement meet physical performance test requirements. Under this specification, six cement types are available: 

• GU (general use). 
• LH (low heat of hydration). 
• MH (moderate heat of hydration). 
• HE (high early strength). 
• MS (moderate sulfate resistance). 
• HS (high sulfate resistance).  

For example, Type MS and HS cements use ASTM C1012, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution, to ensure resistance to sulfate attack. The performance classification of hydraulic cement is thus based on the concept that direct material performance is of interest and not its composition. This approach promotes innovative development of composite portland cements (for example, portland cement blended with limestone or multiple supplementary cementitious materials) as well as opening the door to non-portland cement binders that have the potential to significantly alter the CO2 associated with concrete construction.

As it is a relatively new specification, the acceptance of ASTM C1157 cements is currently mixed. Although the majority of States allow ASTM C1157 cements in their building codes, only a few State departments of transportation (DOTs)—for example, Colorado, Montana, New Mexico, and Utah—accept their use for transportation projects. In time, the use of ASTM C1157 cements has the potential to lower the carbon footprint of concrete significantly while more effectively addressing the specific performance needs of transportation projects.   Download

0 comments :

Loading...
Loading...

Amazon Promote Code

Help & Customer Service

Subscribe to Newsletter

We'll never share your Email address.
© 2015 Needdaily.net. Amazon Run Designed by Amanzon Run. Powered by Amazon Run.